Escherichia coli (E. coli) is a type of bacteria that can cause severe human illness. While there are many types of E. coli bacteria, only certain types cause food borne illness. Hundreds of harmless strains of E. coli can be found widely in nature, including the intestinal tracts of humans and other warm-blooded animals. Disease-causing strains, however, are a frequent cause of both intestinal and urinary-genital tract infections.
In 1982, scientists identified the first harmful food borne strain of E. coli in the United States. The disease-causing food borne E. coli most commonly found in this country is called O157:H7. Cattle are the main sources of E. coli O157:H7, but these bacteria also can be found in other domestic and wild mammals. E. coli serotype O157:H7 is a rare variety of E. coli that produces large quantities of one or more related, potent toxins that cause severe damage to the lining of the intestine.
Several different strains of harmful E. coli can cause diarrheal disease. Particularly dangerous types of E. coli, such as E. coli O157:H7, produce one or more kinds of toxins (poisons) called Shiga toxins. Shiga toxins can severely damage the lining of intestines and kidneys. These types of bacteria are called Shiga toxin-producing E. coli (STEC). STEC often causes bloody diarrhea and can lead to kidney failure in children or in people with weakened immune systems. STEC is also referred to as verocytotoxic E. coli (VTEC) or enterohemorrhagic E. coli (EHEC); these all refer generally to the same group of bacteria. The most commonly identified STEC in North America is E. coli O157:H7 (often shortened to E. coli O157 or even just “O157”).
Enterotoxigenic E. coli (ETEC), which produce a different toxin, can cause diarrhea. These strains typically cause so-called travelers' diarrhea because they commonly contaminate food and water in developing countries. Enteropathogenic E. coli (EPEC) cause persistent diarrhea (lasting 2 weeks or more) and are more common in developing countries where they can be transmitted to humans through contaminated water or contact with infected animals. Other types of E. coli, including O26:H11 and O111:H8, also have been found in the United States and can cause disease in people.
E. coli infection is characterized by severe cramping (abdominal pain) and diarrhea that is initially watery but becomes grossly bloody. Occasionally vomiting occurs. Fever is either low-grade or absent. The illness is usually self-limited and lasts for an average of 8 days. Some individuals exhibit watery diarrhea only.
Hemorrhagic colitis is diagnosed by isolation of E. coli of serotype O157:H7 or other verotoxin-producing E. coli from diarrheal stools. Alternatively, the stools can be tested directly for the presence of verotoxin. Confirmation can be obtained by isolation of E. coli of the same serotype from the incriminated food.
In addition to E. coli O157, many other kinds (called serogroups) of STEC cause disease. These other kinds are sometimes called “non-O157 STEC.” E. coli serogroups O26, 0111, and O103 are the non-O157 serogroups that most often cause illness in people in the United States.
People of any age can become infected with STEC. Very young children and the elderly are more likely to develop severe illness and hemolytic uremic syndrome (HUS) than others, but even healthy older children and young adults can become seriously ill. The symptoms of STEC infections vary for each person but often include severe stomach cramps, diarrhea (often bloody), and vomiting.
Around 5 to 10% of those who are diagnosed with STEC infection develop a potentially life-threatening complication known as hemolytic uremic syndrome (HUS). Clues that a person is developing HUS include decreased frequency of urination, feeling very tired, and losing pink color in cheeks and inside the lower eyelids. Persons with HUS should be hospitalized because their kidneys may stop working and they may develop other serious problems. Most persons with HUS recover within a few weeks, but some suffer permanent damage or die.
STEC live in the guts of ruminant animals, including cattle, goats, sheep, deer, and elk. The major source for human illnesses is cattle. STEC that cause human illness generally do not make animals sick. Other kinds of animals, including pigs and birds, sometimes acquire STEC from the environment and may carry or spread it.